I think this depends on experience to a certain extent, but man that day 7-11 stage has definitely gotten me the most since I have started this. After that, Day 21, Day 30, and 39 were extremely difficult days.
In my case I would've said experience when I first started nofap but now that i've been trying for a while, i'd say days 4-7 are hardest cause that's when urges first start rearing their head
